Transient stabilized cascode biasing

ABSTRACT

A biasing circuit with high current drive capability for fast settling of a biasing voltage to a stacked cascode amplifier is presented. According to a first aspect, the biasing circuit uses transistors matched with transistors of the cascode amplifier to generate a boost current during a transition phase that changes the biasing voltage by charging or discharging a capacitor. The boost current is activated during the transition phase and deactivated when a steady-state condition is reached. According to a second aspect, the biasing circuit uses an operational amplifier in a feedback loop that forces a source node of a cascode transistor of a reference circuit, that is a scaled down replica version of the cascode amplifier, to be at a reference voltage. The high gain and high current capability of the operational amplifier, provided by isolating a high frequency signal processed by the cascode amplifier from the reference circuit, allow for a quick settling of the biasing voltage.

CROSS REFERENCE TO RELATED APPLICATIONS—CLAIM OF PRIORITY

This application is a continuation of commonly owned and co-pending U.S.patent application Ser. No. 16/774,986, filed Jan. 28, 2020, entitled“Transient Stabilized Cascode Biasing”, the disclosure of which isincorporated herein by reference in its entirety. Application Ser. No.16/774,986 is a continuation of commonly owned U.S. patent applicationSer. No. 16/044,378, filed Jul. 24, 2018, entitled “Transient StabilizedCascode Biasing”, now U.S. Pat. No. 10,587,225 issued Mar. 10, 2020, thedisclosure of which is incorporated herein by reference in its entirety.

The present application may be related U.S. Pat. No. 9,843,293, entitled“Gate Drivers for Stack Transistor Amplifiers”, issued on Dec. 12, 2017,the disclosure of which is incorporated herein by reference in itsentirety. The present application may also be related U.S. Pat. No.7,248,120, entitled “Stacked Transistor Method and Apparatus”, issued onJul. 24, 2007, the disclosure of which is incorporated herein byreference in its entirety. The present application may also be relatedU.S. Pat. No. 9,716,477, entitled “Bias Control for Stacked TransistorConfiguration”, issued on Jul. 25, 2017, the disclosure of which isincorporated herein by reference in its entirety. The presentapplication may also be related to U.S. Pat. No. 9,219,445 entitled“Optimization Methods for Amplifiers with Variable Supply Power”, issuedDec. 22, 2015, the disclosure of which is incorporated herein byreference in its entirety. The present application may also be relatedto U.S. Pat. No. 9,413,298, issued Aug. 9, 2016, entitled “AmplifierDynamic Bias Adjustment for Envelope Tracking”, the disclosure of whichis incorporated herein by reference in its entirety. The presentapplication may also be related to U.S. Patent Publication No.2018/0083578, published Mar. 22, 2018, entitled “Cascode Amplifier BiasCircuits”, the disclosure of which is incorporated herein by referencein its entirety.

TECHNICAL FIELD

The present teachings relate to amplifiers used in radio frequency (RF)circuits. In particular, the present application relates to gate biasingfor amplifiers comprising stacked transistors which can operate indifferent modes.

BACKGROUND

In recent years, stacked cascode amplifiers, which use a plurality oftransistors arranged as a stack (stacked transistors) in anamplification stage of the amplifiers, have become predominant in radiofrequency (RF) applications where high power, high voltage outputs aredesired. Due to the higher number of transistors in the stack, voltagehandling performance of the amplifier is increased, thereby allowing thehigh power, high voltage outputs. Stacked or cascoded amplifiers arealso common in low noise amplifiers where the benefits to gain anisolation as well as linearity are realized in addition to voltagehandling. Since the stacked transistors comprise individual low voltagetransistors which can tolerate a voltage substantially lower than theoutput voltage of the amplifier, it is important to bias the low voltagetransistors of the stack so to maintain operation within their tolerablevoltage range. Such voltage compliance of the low voltage transistors ofthe stack must be maintained whether the amplifier operates in an activemode transmitting a signal, or in a standby mode not transmitting asignal. In addition, as performance characteristics of such amplifiersmay be based on the biasing voltages to the transistors of the stack, itis important to quickly stabilize such biasing voltages so to reduce atransition phase between different operating modes of the amplifiers.This in turn can allow reduction in settling times of the amplifier whenswitching, for example, between activated and deactivated states of theamplifier, bands of operation, and/or gain settings of the amplifier,and therefore allow for quicker connections and reduced data loss due tolonger settling times of the amplifier.

FIG. 1 shows a simplified schematic of a prior art stacked cascode (RF)amplifier (100). As shown in FIG. 1 , the stacked cascode amplifier(100) can comprise a stack of n FET transistors (M1, M2, . . . , Mn)that include an input transistor M1, and cascode transistors (M2, . . .Mn), including an output transistor Mn. An input RF signal, RF_(in),provided at an input terminal of the amplifier (100) is routed to a gateof the input transistor, M1, and is amplified by the amplifier (100). Acorresponding amplified output RF signal, RF_(out), is provided at adrain of the output transistor, Mn, and routed to an output terminal ofthe amplifier. Decoupling capacitors (Cin, Cout) can be used to decouplelow frequency (e.g., DC) biasing voltages provided to the stack oftransistors (transistor stack) from the RF_(in) and RF_(out) signals. Asupply voltage, V_(DD), is provided to the drain of the outputtransistor, Mn, through an inductor, L, and a reference potential (e.g.,GND), representing for example an AC ground, is connected to a source ofthe input transistor M1. In some implementations, as for exampledescribed in the above referenced U.S. Patent Publication No.2018/0083578, the disclosure of which is incorporated herein byreference in its entirety, the source of the input transistor may beoptionally connected to the AC ground via degeneration elements, suchas, for example, the degeneration inductor L_(deg) shown in FIG. 1 . Aperson skilled in the art is well aware of such implementations, asused, for example, in design of low noise amplifiers (LNA's) of areceive path of an RF front end system.

With continued reference to FIG. 1 , biasing voltages (Vg2, . . . , Vgn)are provided to gates of the cascode transistors (M2, . . . , Mn)through resistors (R2, . . . , Rn) connected to the gates of the cascodetransistors, and a bias voltage Vg1 is provided to the gate of the inputtransistor M1. Although not shown in FIG. 1 , biasing voltage Vg1 mayalso be provided to the gate of the input transistor via a resistor, asshown, for example, in FIG. 2 . Such resistors may be used, incombination with the gate capacitors (Gg2, . . . , Cgn), to decouple anynoise from a biasing circuit that generates the biasing voltages intothe stacked cascode amplifier and/or decouple any residual RF signal atgates of the cascode transistors (M2, . . . , Mn) from the biasingcircuit. Gate capacitors (Cg2, . . . , Ggn) are coupled between gates ofthe cascode transistors (M2, . . . , Mn) and the reference potential,GND. It should be noted that n is an integer number that can be of anyvalue equal to, or greater than, two. A value of n may be based on avoltage withstand capability of the transistors (M1, M2, . . . , Mn) anda high value of an RF voltage at the drain of the output transistor Mn.More description of such prior art stacked cascode amplifier (100) canbe found, for example, in the above referenced U.S. Pat. No. 7,248,120,the disclosure of which is incorporated herein by reference in itsentirety.

Biasing voltages to the stacked cascode amplifier (100) of FIG. 1 may beprovided by biasing circuits according to various implementations knownin the art. Some such biasing circuits are described, for example, inthe above referenced U.S. Pat. Nos. 9,843,293, 7,248,120, 9,716,477, andU.S. Patent Publication No. 2018/0083578, the disclosures of which areincorporated herein by reference in their entirety. Also, as described,for example, in the above referenced U.S. Pat. No. 9,716,477, the supplyvoltage V_(DD), may be a fixed voltage or a variable voltage. Thevariable voltage may be provided, for example, via a DC-DC converter ora voltage regulator. In some exemplary configurations, the supplyvoltage can vary under control of an external control signal. In someconfigurations, the control signal can be a function of an envelopesignal of the input RF signal, RFin, or the output RF signal, RFout.Detailed description of biasing methods and apparatus for stackedtransistor amplifiers operating from a variable supply voltage can befound, for example, in the above referenced U.S. Pat. Nos. 9,219,445,and 9,413,298, the disclosures of which are incorporated herein byreference in their entirety.

FIG. 2 shows an exemplary prior art biasing circuit (210) that providesa biasing voltage, Vg2, to the gate of the cascode transistor M2 for anexemplary case of a stacked cascode amplifier (M1, M2) with anon-limiting height of n=2. It should be noted that as discussed abovein relation to the stacked cascode amplifier (100) of FIG. 1 , suchheight can be represented by any number n that is equal to, or greaterthan, two. Accordingly, each of the gate voltages to the cascodetransistors (M2, . . . , Mn) may be provided via a biasing circuit thatis similar to one depicted in FIG. 2 (e.g., FIG. 5A later described).Also, not shown in FIG. 2 , is biasing of the gate of the inputtransistor, M1, which is beyond the scope of the present disclosure, andwhich may be provided independently from the biasing voltage Vg2. Someexemplary biasing circuits for biasing the gate of the input transistor,M1, can be found, for example, in the above referenced U.S. Pat. No.9,716,477 and U.S. Patent Publication No. 2018/0083578, the disclosuresof which are incorporated herein by reference in their entirety.

As can be seen in FIG. 2 , the biasing circuit (210) comprises a currentmirror branch formed by a reference cascode circuit (M′1, M′2) that is ascaled down (e.g., 1/20^(th) or less, such as, for example, 1/30^(th),1/40^(th), . . . , 1/Nth with N≥20) replica version of the cascodeamplifier circuit (M1, M2), so that a current (Icore) flowing throughthe transistors (M′1, M′2) is mirrored to provided a current (Icore*N)flowing thorough the transistors (M1, M2). The transistors M′1 and M′2are smaller size versions of the transistors M1 and M2 respectively, sothat for same biasing voltages applied to the amplifier circuit (M1, M2)and the reference circuit (M′1, M′2), a ratio of the biasing currentsthrough the reference circuit (M′1, M′2) and the amplifier circuit (M1,M2) is substantially equal to a ratio of the sizes of the transistors ofthe two circuits. Accordingly, if a current Icore flows through thereference circuit (M′1, M′2), then a current Icore*N flows through theamplifier circuit (M1, M2), where N is a ratio of the size of theamplifier circuit to the size of the reference circuit, or in otherwords, N is a scaling factor between the two circuits. For example, ifthe transistors M′1, M′2 of the cascode reference circuit (M′1, M′2) are1/100 of the size of the transistors M1, M2 of the cascode amplifier(M1, M2) respectively, the scaling factor N would be 100. It should benoted that the size of such transistors may be defined in terms ofdifferent aspects of the transistors, such as, for example, transistorarea, gate length, gate width, etc., so long as a same aspect of thetransistors is compared.

With further reference to FIG. 2 , gate voltage Vg2 for biasing of thecascode transistor M2 is provided via a combination of a resistivevoltage divider (Rtop, Rbot), a diode-connected transistor, M_Diode, andcurrent sources IcasP and IcasN. The current source IcasP is coupled toa common gate-drain node of the diode-connected transistor, M_diode, andthe current source IcasN is coupled to a source node of thediode-connected transistor, M_diode. The resistive voltage divider(Rtop, Rbot) generates a reference voltage, Vref2, at the source node ofthe diode-connected transistor, M_diode, based on a supply voltageV_(DD). In turn, the diode-connected transistor, M_diode, generates thegate voltage, Vg2, that is one diode drop above the reference voltage,Vref2. Finally, current from IcasP or IcasN serve to provide a currentfor the diode connected transistor M_diode and also charge or dischargethe Vg2 node such that Vg2 is equal to Vref2+Vdiode, where Vdiode is thevoltage across the diode-connected transistor M_diode.

With continued reference to FIG. 2 , by selecting the diode-connectedtransistor, M_diode, to have a same current density as the cascodetransistors M′2 and M2, a person skilled in the art would understandthat in a steady-state condition of the circuit shown in FIG. 2 , wherethe reference voltage, Vref2, provided by the resistive voltage divider(Rtop, Rbot) and the gate voltage Vg2 are steady, a gate-to-sourcevoltage, Vgs, of the diode-connected transistor, M_diode, is equal to agate-to-source voltage, Vgs, of the cascode transistors M′2 and M2. Inturn, this allows to precisely set, for example, a drain voltage of theinput transistor M1 to be equal to the reference voltage, Vref2. As usedherein, and as it is well known to a person skilled in the art, theexpression “current density” refers to a ratio of a current through atransistor (e.g., drain current) to a size of the transistor, where thesize can be any of a transistor area, a gate length, a gate width, etc.

During the steady-state condition of the circuit shown in FIG. 2 , thevoltage Vref2 and the voltage Vg2 are substantially fixed, and thereforeno current flows into the gate capacitor Cg2 and no current flows fromthe source of the diode-connected transistor M_diode into the resistivevoltage divider (Rtop, Rbot). Accordingly, the currents IcasP and IcanNare equal.

Considering a transition phase of the circuit shown in FIG. 2 , definedby a change of the biasing voltage Vg2 corresponding to a desiredoperation of the cascode amplifier (M1, M2). Such transition phase maycorrespond to, for example, an activation state of the amplifier after adeactivation state of the amplifier, or a change in a frequency band(and therefore operating frequency) of the amplifier, or a change in again of the amplifier. As the reference voltage, Vref2, sets the biasingvoltage, Vg2, such transition phase may include changing values of theresistors Rtop and/or Rbot so to change the reference voltage, Vref2. Ascan be seen in FIG. 2 , such resistors may be programmable/settableresistors, either according to discrete values or continuous values. Itshould be noted that although in the exemplary case of the prior artconfiguration of FIG. 2 , a resistive voltage divider is used togenerate the reference voltage, Vref2, a person skilled in the art wouldknow that other circuit implementations may also be used, such as, forexample, circuits using an operational amplifier and/ordigital-to-analog devices. Furthermore, in a case where the transitionphase corresponds to activation of the amplifier after a deactivation,or vice versa, the transition phase may also includeactivation/deactivation of the current sources (e.g., Icore, IcasP,IcasN) which may have been turned off during the deactivated states ofthe cascode amplifier (M1, M2) for power conservation purposes.

During the transition phase of the circuit shown in FIG. 2 , currentfrom IcasP may flow into the gate capacitor, Cg2, to charge up thecapacitor to a new (higher) voltage value of Vg2. Alternatively, acurrent may flow from the capacitor Cg2 into the diode-connectedtransistor to discharge the capacitor for a new (lower) voltage value ofVg2. For this, a maximum current available for the charging ordischarging of the capacitor Cg2 is provided by the maximum current ofthe current source IcasP and the maximum current of the current sourceIcasN respectively. As such maximum currents are set to be sufficientlylow so as to not drain substantial power from the supply V_(DD) (andtherefore from a battery generating V_(DD)), charging and dischargingspeed of the capacitor Cg2, and therefore settling time of theamplifier's biasing conditions, may be compromised in favor of lesserpower consumption of the circuit. A motivation for the teachingsaccording to the present disclosure is to remove a need for suchcompromise, and therefore reduce the settling times while maintaining alow power consumption of the circuit.

SUMMARY

According to a first aspect of the present disclosure, a circuitarrangement is presented, the circuit arrangement comprising: a stackedcascode amplifier comprising an input transistor and one or more cascodetransistors, the one or more cascode transistors comprising an outputtransistor, wherein the input transistor is configured to receive an RFsignal and the output transistor is configured to output an amplifiedversion of the RF signal; a reference circuit that is a scaled downversion of the stacked cascode amplifier, the reference circuit coupledto the stacked cascode amplifier via respective gate nodes; and abiasing circuit configured to provide a biasing voltage to at least onegate node of a transistor of the one or more cascode transistors and agate node of a respective transistor of the reference circuit, whereinthe biasing circuit comprises a feedback loop that senses a voltage at asource node of the respective transistor of the reference circuit andcontrols the biasing voltage so that a sensed voltage at said sourcenode is equal to a reference voltage.

According to second aspect of the present disclosure, a method forbiasing a stacked cascode amplifier is presented, the method comprising:providing a reference circuit that is a scaled down version of thestacked cascode amplifier; coupling gate nodes of the stacked cascodeamplifier to respective gate nodes of the reference circuit viarespective resistors; based on the coupling, isolating an RF signalprocessed by the stacked cascode amplifier from the reference circuit;and controlling, via a feedback loop with higher gain, a biasing voltageto a gate node of a cascode transistor of the stacked cascode amplifierbased on a voltage sensed at a source node of a respective transistor ofthe reference circuit, wherein the higher gain is provided by theisolating.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated into and constitute apart of this specification, illustrate one or more embodiments of thepresent disclosure and, together with the description of exampleembodiments, serve to explain the principles and implementations of thedisclosure.

FIG. 1 shows a simplified schematic of a prior art stacked cascode (RF)amplifier.

FIG. 2 shows an exemplary prior art biasing circuit that provides abiasing voltage, Vg2, to a gate of a cascode transistor of a stackedcascode amplifier.

FIG. 3A shows a biasing circuit according to an embodiment of thepresent disclosure comprising a current boost circuit that can beselectively activated to provide a current boost for a shorter settlingtime of a biasing voltage at a gate of a cascode transistor of a stackedcascode amplifier.

FIG. 3B shows a biasing circuit according to an embodiment of thepresent disclosure comprising a programmable current boost circuit thatcomprises a plurality of individual current boost circuits that can beselectively and independently activated to provide different combinedcurrent boosts for a desired settling time of a biasing voltage at agate of a cascode transistor of a stacked cascode amplifier.

FIG. 3C shows graphs representing an exemplary pulse timing provided toa plurality of current boost circuits and a resulting combined currentboost of the programmable current boost circuit of FIG. 3B.

FIG. 3D shows graphs representing exemplary different pulse timingsprovide to a plurality of current boost circuits and a resultingcombined current boost of the programmable current boost circuit of FIG.3B.

FIG. 4A shows a biasing circuit according to an embodiment of thepresent disclosure based on the embodiment depicted in FIG. 3A, where aswitch is used to couple and decouple the current boost circuit to andfrom the biasing circuit.

FIG. 4B shows graphs representing control timing for the switch SW1relative to the control timing for current boost circuit (350) of thebiasing circuit (410) shown in FIG. 4A.

FIG. 5A shows a biasing circuit according to an embodiment of thepresent disclosure based on the embodiment depicted in FIG. 3A, wherethe biasing voltage is provided to a gate of an output transistor of thestacked cascode amplifier.

FIG. 5B shows a biasing circuit according to an embodiment of thepresent disclosure based on the embodiment depicted in FIG. 3A, wheresimilar biasing circuits are used to provide biasing voltages to gatesof a plurality of cascode transistors of the stacked cascode amplifier.

FIG. 6 shows a biasing circuit according to an embodiment of the presentdisclosure comprising a feedback loop to generate a biasing gate voltageof a cascode transistor of a stacked cascode amplifier.

FIG. 7 shows a biasing circuit according to an embodiment of the presentdisclosure based on the embodiment depicted in FIG. 6 , where similarbiasing circuits are used to provide biasing voltages to gates of aplurality of cascode transistors of the stacked cascode amplifier.

FIG. 8 shows a biasing circuit according to an embodiment of the presentdisclosure based on the embodiment depicted in FIG. 6 , where thebiasing gate voltage is provided to a gate of a cascode transistor of astacked cascode amplifier having a plurality of cascode transistors.

DETAILED DESCRIPTION

Throughout this description, embodiments and variations are describedfor the purpose of illustrating uses and implementations of theinventive concept. The illustrative description should be understood aspresenting examples of the inventive concept, rather than as limitingthe scope of the concept as disclosed herein.

The present disclosure describes electrical circuits in electronicdevices (e.g., cell phones, radios) having a plurality of devices, suchas for example, transistors (e.g., MOSFETs). Persons skilled in the artwill appreciate that such electrical circuits comprising transistors canbe arranged as amplifiers.

FIG. 3A shows a biasing circuit (310 a) according to an embodiment ofthe present disclosure, based on the biasing circuit (210) describedabove in relation to FIG. 2 , further comprising a current boost circuit(350) that can be selectively activated to provide a current boost for ashorter settling time of the biasing voltage, Vg2, provided to the gateof the cascode transistor, M2, of the stacked cascode amplifier (M1,M2). The current boost circuit (350) comprises a diode-connectedtransistor, M_Diode*M, and current sources IcasP*M and IcasN*M, where“*M” denotes a multiplicative size factor (i.e., scaling factor) withreference to corresponding elements M_Diode, IcasP and IcasN of thebiasing circuit (310 a). The current source IcasP*M is selectivelycoupled (and decoupled) to a common gate-drain node of thediode-connected transistor, M_diode*M, via a switch, FCOS11, and thecurrent source IcasN*M is selectively coupled (and decoupled) to asource node of the diode-connected transistor, M_diode*M, via a secondswitch, FCOS21. A person skilled in the art would realize that when theswitches FCOS11 and FCOS21 are closed, the biasing circuit (310 a) ofFIG. 3A provides a same functionality as the biasing circuit (210) ofFIG. 2 but with added current charging and discharging capability. Inother words, as related to the charging capability of the gate capacitorCg2, the biasing circuit (310 a) according to the present teachings canbe considered as a scaled up version (i.e., scale factor (M+1)/1) of thebiasing circuit (210) of FIG. (210) when the switches FOCS1 and FCOS21are closed, and a same scale version of the circuit (210) of FIG. (210)when the switches FOCS1 and FCOS21 are open.

According to an embodiment of the present disclosure, the currentdensity of the diode-connected transistor M_diode*M is selected to besame as the current density of the diode-connected transistor M_diode.Accordingly, in the activated state of the current boost circuit (350)provided by closing of the switches FCOS11 and FCOS21, due to the samecurrent densities and the scaling factor, *M, drain voltage V′g2 at thecommon gate-drain node of the diode-connected transistor M_diode*M isequal (substantially equal) to the drain voltage Vg2 at the commongate-drain node of the diode connected transistor M_diode. This allowsactivating and deactivating of the current boost circuit (350) withoutaffecting the gate voltage Vg2.

With further reference to the current boost circuit (350) of FIG. 3A,when activated, boosts of current provided by IcasP*M and by IcasN*M cancombine with currents provided by IcasP and IcasN to respectively chargeand discharge the gate capacitor Cg2, and thereby reducing a settlingtime of the gate voltage Vg2. Once settled, the current boost circuit(350) may be deactivated by opening the switches FCOS11 and FCOS21without affecting or perturbing the gate voltage Vg2 as described above.When the gate voltage Vg2 has settled, the circuit depicted in FIG. 3Ais basically in a steady-state condition and essentially no currentflows in or out the gate capacitor Cg2.

According to an embodiment of the present disclosure, activation of thecurrent boost circuit (350) may be provided via a pulse signal thatcontrols the switches FCOS11 and FCOS21, the pulse signal having a timeduration so to allow charging or discharging of the gate capacitor Cg2to a desired value of the gate biasing voltage, Vg2, in view of theavailable current boost. According to an embodiment of the presentdisclosure, such time duration may be programmable and controlled by asignal aware controller, such as, for example, a transceiver unit (notshown) as is well known in the art. Activation of the current boostcircuit (350) may be based on different conditions of operation of thecascode amplifier (M1, M2) that are obtained through, for example,switching from a deactivated amplifier to an activated amplifier, orswitching from one frequency band of operation to another, or switchingfrom one gain setting of the amplifier to another, which conditions maydictate different amounts of charging or discharging of the gatecapacitor, Cg2, to provide a corresponding gate voltage Vg2.Programmability of the pulse time duration may therefore allow to reducewasted energy by deactivating the current sources IcasP*M and IcanN*M ata time immediately after a time required for settling of the gatevoltage Vg2.

With continued reference to the current boost circuit (350) of FIG. 3A,according to an embodiment of the present disclosure, closing andopening of the switches FCOS11 and FCOS21 is performed in synchrony soto reduce any deviation in voltage at the common gate-drain node V′g2with respect to the voltage Vg2. A person skilled in the art clearlyrealizes that during a transient condition associated with opening orclosing of the switches FCOS11 and FCOS21, current may flow through aconduction path provided between the nodes V′g2 and Vg2 until a steadystate condition is reached where no current flows between the two nodes.Accordingly, although the two nodes V′g2 and Vg2 are electricallyconnected, they may assume different voltage-current behaviors duringtransient conditions. Additionally, the closing of the switches FCOS11and FCOS21, and therefore activation of the current boost circuit (350),may be in synchrony with a change in the condition of operation of thecascode amplifier (M1, M2). Such change in the condition of operationmay include a change in the value of the reference voltage, Vref2,and/or activation of the current source, Icore, and/or a change in anyother parameters that affect operation of the circuit shown in FIG. 3A.Such change in the condition of operation may be based on a decisionperformed by the same signal aware controller (e.g., a transceiver) thatgenerates the pulse signal to control the switches FCOS11 and FCOS21.

FIG. 3B shows a biasing circuit (310 b) according to an embodiment ofthe present disclosure comprising a programmable current boost circuit(350 n) that comprises a plurality of individual current boost circuits(350) similar to one described above with reference to FIG. 3A, arrangedin a parallel configuration. Each such current boost circuit (350) canbe selectively and independently activated via respective switches(FCOS1 k, FCOS2 k) to provide different combined current boosts for adesired settling time of a biasing voltage Vg2 at the gate of a cascodetransistor M2 of a stacked cascode amplifier (M1, M2). Principle ofoperation of each of the current boost circuits (350) of theprogrammable current boost circuit (350 n) is same as described above. Aperson skilled in the art would clearly understand that concurrentactivation of a plurality of such current boost circuits (350) resultsin corresponding currents to combine (i.e., via summation of currents)at the common node V′g2, and therefore allow, based on a number ofconcurrent activated current boost circuits (350), to charge anddischarge the gate capacitor Cg2 according to a programmable current. Inother words, the biasing circuit (310 b) of the present teachings allowsfor a programmable settling time of the gate voltage Vg2.

With continued reference to the biasing circuit (310 b) of FIG. 3B,according to an exemplary embodiment of the present disclosure,activation and deactivation of each of the plurality of current boostcircuits (350) may be selectively performed by a same pulse signal, ordifferent pulse signals with same, or essentially same, edge timings. Inother words, when a group of the current boost circuits (350) isactivated, they provide, in combination, a constant current boost forcharging or discharging the gate capacitor Cg2. This allows for asubstantially same behavior as provided in the biasing circuit (310 a)of FIG. 3A, with the difference that a value of the current boost can beprogrammatically changed. FIG. 3C shows pulse timing and resultingcombined current boost for such configuration for an exemplary casewhere three current boost circuits (350) are selected, each providing aboost of current Il, 12 and 13.

With further reference to the biasing circuit (310 b) of FIG. 3B,according to another exemplary embodiment of the present disclosure,activation and deactivation of each of the plurality of current boostcircuits (350) may be selectively performed by a different pulse signalhaving one or both of a rising edge and a trailing edge at differenttimings. This allows to shape a charging and/or discharging profile ofthe capacitor Cg2 by providing a current boost that varies with time, asshown in FIG. 3D. FIG. 3D shows three different pulse timings foractivation of respective three current boost circuits (350), eachproviding a respective current boost Il, 12 and 13. A resulting combinedcurrent boost provides a profile for charging of the gate capacitor Cg2.A person skilled in the art would clearly realize that such profile canbe of any shape and function of activation and deactivation of differentcurrent boost circuits (350) during the charging of the capacitor Cg2.It should be noted that although in the exemplary case depicted in FIG.3D all three current boost circuits (350) are activated at a same starttime, a person skilled in the art would clearly realize that any orderof activation/deactivation timing for a selected current boost circuit(350) for charging of the gate capacitor Cg2 may be envisioned.

With reference back to FIG. 3A, a person skilled in the art wouldrealize that when the current boost circuit (350) is first activated,which may also include activation of corresponding current sources IcasPand IcasN, a time for setting of such current sources may be different(e.g., active state currents reached at different times, or two switchesclosed at different times) which can therefore induce undesiredperturbations of the voltage at node Vg2, bringing such voltage to alevel different from one set by the reference voltage, Vref2. Likewise,when the current boost circuit (350) is deactivated, which may alsoinclude deactivation of the current sources IcasP and IcasN, a turn offtime of such current sources may be different (e.g., deactivated statecurrents reached at different times, or two switches open at differenttimes) which can also induce perturbations of the voltage at node Vg2,bringing such voltage to a level different from one set by the referencevoltage, Vref2. The voltage perturbation related to the activation ofthe current boost circuit (350) may be considered of a lesser impactsince a boost current follows to quickly settle the voltage at node Vg2,and therefore at the gate of the cascode transistor M2, to the desiredvalue. However, in the case of the voltage perturbation related to thedeactivation of the current boost circuit (350), since no current boostis available, a larger settling time may be required to bring thevoltage at node Vg2 back to the desired value. It follows that accordingto an embodiment of the present disclosure, coupling and decoupling ofthe current boost circuit (350) to the node Vg2 may be performed by aswitch, SW1, as shown in FIG. 4A.

FIG. 4A shows a biasing circuit (410) according to an embodiment of thepresent disclosure based on the biasing circuit (310 a) depicted in FIG.3A, where a switch, SW1, is used to selectively couple and decouple thecurrent boost circuit (350′) to and from the node Vg2 of the biasingcircuit. Such added switch, SW1, can be used to couple the current boostcircuit (350′) to the node Vg2, and therefore to the gate of the cascodetransistor M2, only when the current boost circuit (350′) is activated(switches FOCS1, FOCS2 closed) and is at a stable operating condition,provided for example, to a same open or close state of the switchesFOCS1 and FOCS2, and/or a same current sourced and sinked by the currentsources IcasP and IcasN. In order to reduce any transients due tomismatch of voltages at nodes V′g2 and Vg2 prior to the closing of theswitch SW1, voltages at such nodes are equalized by controlling thevoltage at node V′g2 through a resistive voltage divider (R′_(top),R′_(bot)) in a manner similar to the controlling of the voltage at nodeVg2 through the resistive voltage divider (R_(top), R_(bot)) describedabove. Furthermore, in order to also equalize effect of current flowfrom the diode connected transistors M_diode and M_diode*M through therespective resistive voltage dividers (R_(top), R_(bot)) and (R′top,R′_(bot)) during transient or mismatch conditions (e.g., mismatchbetween top (IcasP, IcasP*M) and bottom (IcasN, IcasN*M) currentsources), according to an embodiment of the present disclosure, valuesof the resistors R′_(top) and R′_(bot) are chosen such thatR′_(top)=R_(top)/M and R′_(bot)=R_(bot)/M. Such selection of theresistor values can cause voltages at nodes Vg2 and V′g2 to track duringthe transient and/or mismatch conditions.

FIG. 4B shows graphs representing control timing for the switch SW1relative to the control timing for current boost circuit (350) of thebiasing circuit (410) shown in FIG. 4A. As can be seen in FIG. 4B, theControl Pulse signal during which the current boost circuit (350′) isactivated starts at a time to, representing a start activation time ofthe current boost circuit (350′) which can coincide with a time for achange in condition of operation of the cascode amplifier (M1, M2). Atthis time, the switches FCOS11 and FCOS21 are controlled to close (andthe reference voltage, Vref2, controlled to change to a new value) andthe current sources IcasN and IcasP may be activated. During the timeperiod [t₀, t₁[the switch SW1 remains open so to allow the current boostcircuit (350′) to settle. A settling time of the current boost circuit(350′) may be derived, for example, via circuit simulation and testing.At time t₁, the current boost circuit has settled to its nominaloperating condition, the reference voltage Vref2 has a new value, andthe switch SW1 is closed. Closing of the switch SW1 may starts injectionof a boost current (positive or negative) from the current boost circuit(350′) into the gate capacitor Cg2 so to charge (or discharge) thecapacitor to a nominal value set by Vref2. At time t₃, the capacitor Cg2is fully charged and the gate voltage Vg2 is at its nominal value. Attime t₃, the switch SW1 is opened so to decouple the current boostcircuit (350′) form the gate of the cascode transistor M2, and thereforeisolate the gate from any voltage perturbations related to thedeactivation of the current boost circuit (350′). At time t₄, thecurrent boost circuit (350′) is deactivated, including opening of theswitches FCOS11, FCOS21, and may be further deactivating of the currentsources IcasN and IcasP. It should be noted that although the additionof the switch SW1 according to the present teachings depicted in FIG. 4Ais shown relative to a biasing circuit (410) having a single currentboost circuit (350′), for the same reasons described above, a similarswitch can be used when the biasing circuit has a plurality of parallelcurrent boost circuits (350′) as shown for the programmable currentboost circuit (350 n) of FIG. 3B. In this case, the switch SW1 can bepositioned between the node V′g2 of the programmable current boostcircuit (350 n) and the node Vg2. In such configuration, timing for theclosing and opening of the switch SW1, respectively t₁ and t₂ of FIG.4B, can be relative to a timing to and t₃ as shown in FIG. 4B,respectively corresponding to a start of activation of a first currentboost circuit (350′) and start of deactivation of a last current boostcircuit (350′) of the programmable current boost circuit (350 n).

As described above, the cascode amplifier used in the variousembodiments according to the present disclosure is not restricted to acascode amplifier (M1, M2) with a stack height of two, having a singlecascode transistor, M2, as shown in the exemplary embodiments of FIGS.2-4 , rather, any stack height for the cascode amplifier can beenvisioned, as shown in FIG. 5A. In this case, one or more of the gatevoltages (Vg2, . . . , Vgn) can be generated via a circuit similar toone described above in reference to FIGS. 2-4 , where a current boostcircuit (350) is used to reduce settling time of the gate voltages. Inthe exemplary embodiment according to the present disclosure shown inFIG. 5A, a biasing circuit (550 n) comprising a current boost circuit(350) is used to generate the gate voltage Vgn for the output transistorMn of the cascode amplifier (M1, M2, . . . , Mn). Principle of operationof the biasing circuit (550 n) can be clearly derived from the abovedescription. In this case, a reference voltage, Vrefn, set via, forexample, a resistive divider, determines a value of the gate voltage,Vgn, which is obtained by charging the gate capacitor Cgn via thecurrent boost circuit (350). It should be noted that the current boostcircuit (350) may be a programmable current boost circuit (350 n) asdescribed above with reference to FIG. 3B. As shown in FIG. 5B, similarbiasing circuits (5502, . . . , 550 n) can be used for generation of thegate voltages (Vg2, . . . , Vgn).

With reference back to the prior art configuration depicted in FIG. 2and as described above, the diode-connected transistor M_diode isselected to have a same current density as the cascode transistors M′2and M2. Also, in view of a desired low current consumption of thebiasing circuit (210) during the steady-state condition, a (standby)current through the diode-connected transistor M_diode is selected to bemuch smaller than currents through the reference circuit (M′ 1, M′2) andthe amplifier circuit (M1, M2). For, example, such (standby) current canbe in the order of 75 μA, and may be obtained via a transistor (i.e.,M_diode) with a basic geometry (e.g., gate width, gate length) that isdifferent from a basic geometry used in the cascode transistors of thereference and amplifier circuits. Such requirement for same currentdensities while maintaining a low current consumption during thesteady-state condition may be accomplished by first selecting the lowcurrent value, and then sizing the diode-connected transistor, M_diodeto have the desired current density. In turn, this may result in thediode-connected transistor, M_diode, to have a gate width which is afraction of a gate width used in the cascode transistors. For example,the cascode transistors (M′2, M2) may have one or a plurality of gates,each gate having a same width of about 4 μm, whereas the diode-connectedtransistor, M_diode, may be a single finger transistor having a gatewith a width of 1.2 μm for a corresponding low current of about 75 μA. Aperson skilled in the art would realize that not having same basicgeometries in the transistors of the configuration depicted in FIG. 2may result in a suboptimal matching of the transistors and therefore ina reduced tracking of the circuits with respect to parametersvariability, such as, for example, process and temperature variations.In other words, due to the suboptimal matching, parameters variabilitymay result in unequal tracking of the currents through the currentsources IcasP and/or IcasN with respect to the currents through (M′1,M′2) and (M1, M2), and therefore may result in errors in the gatebiasing voltage, Vg2. Such errors in the gate biasing voltage, Vg2, mayin turn affect performance of the cascode amplifier (M1, M2), such as,for example, linearity and gain. It should be noted that a personskilled in the art is well aware of the concept of transistor matchingwhich can result in perfect tracking of current densities of the matchedtransistors with respect to parameters variability (e.g., process,temperature). When matched, currents through the matched transistors arealways equal to the ratios of the sizes of the matched transistors.Perfect matching may be provided through usage of the same geometriesfor the matched transistors.

With further reference to the prior art configuration of FIG. 2 , theabove discussed suboptimal matching can also introduce unequal trackingin currents through the IcasP and IcasN current sources, which in turncan generate a difference current (e.g., IcasP−IcasN) to flow in theresistive voltage divider (Rtop, Rbot) that can affect value of thereference voltage, Vref2. Accordingly, values of the resistors Rtop andRbot are chosen to be low enough so that a current through suchresistors during the steady-state condition is substantially equal to,or within the same order of magnitude of, the current through thediode-connected transistor, M_diode (e.g., nominal currents of thecurrent sources IcasP, IcasN). This in turn can minimize an impact on avalue of the reference voltage, Vref2, based on the flow of thedifference current through the resistive voltage divider (Rtop, Rbot),but at the cost of a higher current through the resistive voltagedivider.

Accordingly, it may be desirable to provide an alternative embodiment tothe biasing circuit (210) of FIG. 2 , such as the embodiment shown inFIG. 6 , which can provide a high current during the transition phase, alow current during the steady-state condition, including a low currentflowing in the resistive voltage divider, and not relying on a perfectmatching of the transistors. FIG. 6 shows a biasing circuit (610)according to an embodiment of the present disclosure comprising afeedback loop realized around an operational amplifier (op-amp), OP2, togenerate a gate voltage, Vg2, of a cascode transistor, M2, of a stackedcascode amplifier (M1, M2). Contrary to the prior art configurationdepicted in FIG. 2 , the present embodiment does not rely on matchedtransistors (e.g., M_diode) to set the gate voltage Vg2. Instead, anoperational amplifier, OP2, is used to force a voltage at a source nodeof the cascode transistor M′2 of the reference circuit (M′ 1, M′2) to beequal to a reference voltage, Vref2, set, for example, via a resistivevoltage divider (Rtop, Rbot).

As can be seen in FIG. 6 , the positive input, Vp, of the op-amp, OP2,is connected to a common node of the two resistors (Rtop, Rbot) forprovision of the reference voltage, Vref2, and the negative input, Vn,of the op-amp, OP2, is connected to the source node of the cascodetransistor M′2, to provide a feedback loop that controls the outputnode, Vg2, of the op-amp, OP2, so that the source node of the cascodetransistor M′2 remains equal to Vp=Vref2. This in turn controls thegate-to-source voltage of the cascode transistor M′2 so to maintain thecurrent Icore flowing through the reference circuit (M′ 1, M′2), andtherefore a current Icore*N through the staked cascode amplifier (M1,M2). Since the op-amp, OP2, can have an infinite gain (e.g., very largegain) as well as a high output current drive capability (sourcing andsinking), its output node, Vg2, coupled to the gate of the cascodetransistors (M′2, M2), can quickly respond to a change in the referencevoltage, Vref2, and quickly charge or discharge the gate capacitor, Cg2.

With continued reference to FIG. 6 , because feedback is provided viasensing of the source node of the cascode transistor M′2, which is sameas the drain node of the cascode transistor M′1, and because an RFsignal processed (amplified) by the amplifier circuit (M1, M2) issubstantially decoupled from the reference circuit (M′1, M′2), a highbandwidth (i.e., high response) of the op-amp, OP2, can be implementedwithout consideration of a frequency of the RF signal. Therefore, a fastsettling time of the gate voltage Vg2 can be obtained, mainly based onthe high slew rate of the op-amp and its high current drivingcapability. In other words, isolation of the RF signal processed by theamplifier circuit (M1, M2) from the reference circuit (M1, M′2) by wayof the resistors (R1, R2) allows for a higher gain of the feedback loopprovided by the op-amp OP2. It should be noted that a person skilled inthe art is well aware of many design techniques to implement the op-amp,OP2, including, for example, design for low standby current (e.g., about60 μA or less), high current sourcing/sinking capability (e.g., sourcefollower output stage), and high slew rate, which design techniques areoutside the scope of the present disclosure.

With continued reference to FIG. 6 , as the reference circuit (M′ 1,M′2) is a scaled down replica (e.g., 1/20^(th) or less, such as, forexample, 1/30^(th), 1/40^(th), . . . , 1/Nth with N≥20) version of theamplifier circuit (M1, M2), with the current (Icore*N) through theamplifier circuit (M1, M2) provided via mirroring of the current (Icore)through the reference circuit (M′1, M′2), as described above withreference to the prior art configuration depicted in FIG. 2 , thecascode transistors M′2 and M2 have a same gate-to-source voltage andtherefore the source of cascode transistor M2 is also equal to Vref2. Itshould be noted that as discussed above with reference to FIG. 2 , samebiasing voltages may be applied to the amplifier circuit (M1, M2) andthe reference circuit (M′1, M′2), and a ratio of the biasing currentsthrough the reference circuit (M′1, M′2) and the amplifier circuit (M1,M2) may be substantially equal to a ratio of the sizes of thetransistors of the two circuits (e.g., Icore*N/Icore=N).

With further reference to the biasing circuit (610) of FIG. 6 , a personskilled in the art would clearly understand that substantially zerocurrent flows from the resistive voltage divider (Rtop, Rbot) into thepositive input, Vp, of the op-amp, OP2. Therefore, resistor valuesR_(top) and Rbot can be selected to be very large so that a very lowcurrent flows into the resistive voltage divider (Rtop, Rbot). Accordingto an exemplary embodiment of the present disclosure, such resistors areselected so a current of about 1 μA or less (e.g., less than 1 μA) flowsthrough the resistive voltage divider (Rtop, Rbot). A person skilled inthe art would appreciate such reduction in current provided by thepresent teachings when compared to the current required in the operationof the prior art configuration of FIG. 2 described above (e.g., 75 μA).Furthermore, a person skilled in the art would appreciate that selectionof the resistor values Rtop and Rbot can provide an arbitrary lowcurrent flow through the resistive voltage divider (Rtop, Rbot) that isindependent from a current sourced or sinked by the op-amp OP2 to chargeor discharge the gate capacitor Cg2.

As it is well known to a person skilled in the art, industry trend mayfavor lower V_(DD) supply voltages which may be limited in the prior artconfiguration of FIG. 2 due to a voltage headroom required for operationof the current source circuit IcasP. Such voltage headroom, which may beabout 200 mV, is necessary for the current source circuit IcasP tooutput a constant nominal current. On the other hand, in the embodimentaccording to the present teachings shown in FIG. 6 , the op-amp, OP2,does not require such headroom and therefore the biasing circuit (610),including the op-amp, OP2, may operate on a lower supply voltage,V_(DD), when compared to the prior art biasing circuit (210) shown inFIG. 2 .

As described above, the cascode amplifier used in the variousembodiments according to the present disclosure is not restricted to acascode amplifier (M1, M2) with a stack height of two, having a singlecascode transistor, M2, as shown in the exemplary embodiment of FIG. 6 ,rather, any stack height for the cascode amplifier can be envisioned.FIG. 7 shows an exemplary embodiment according to the presentdisclosure, where a biasing circuit (710), based on the biasing circuit(610) of FIG. 6 , is used to provide biasing voltages Vg2, Vg3, Vg4, togates of a cascode amplifier circuit (M1, M2, M3, M4) having a stackheight of four.

As can be seen in FIG. 7 , source nodes of each of the cascodetransistors (M′2, M′3, M′4) of the reference circuit (M′ 1, . . . , M′4)is forced to take a value of a respective reference voltage (Vref2,Vref3, Vref4) generated by respective nodes of a resistive voltagedivider (Rd1, . . . , Rd4) coupled to respective positive inputs (Vp2,Vp3, Vp4) of respective op-amps (OP2, OP3, OP4). In other words, eachgate-to-source voltage of the cascode transistors (M′2, M′3, M′4) iscontrolled via a feedback loop similar to one described above withrespect to the configuration (600) depicted in the FIG. 6 .

FIG. 8 shows an exemplary biasing circuit (810) according to anembodiment of the present disclosure based on the embodiment depicted inFIG. 6 , where a biasing gate voltage, Vgk, is provided to a gate of acascode transistor, Mk, of a stacked cascode amplifier (M1, . . . , Mk,. . . , Mn) having a plurality of cascode transistors M2 . . . , Mk, . .. , Mn. Principle of operation of the biasing circuit (810) forgenerating of the gate voltage, Vgk, is similar to one described abovewith reference to generation of Vg2 gate voltage of FIG. 6 , where theop-amp, OPk, is used in a feedback loop to force a source node of acascode transistor, M′k, of the reference circuit (M′1, . . . , M′k, . .. , M′n) to be equal to a reference voltage, Vpk, and accordinglycontrol the gate voltage, Vgk. Based on the embodiments according to thepresent teachings depicted in FIGS. 6, 7 and 8 , a person skilled in theart would clearly understand that for any one or more of the gatevoltages Vg2, . . . , Vgn, generation of a gate voltage of a cascodeamplifier (M1, . . . , Mn), where n can be any integer equal to, orgreater than, two, can be accomplished by an amplifier operating infeedback loop to force a source voltage to a reference voltage andaccordingly control the gate voltage. It should be noted that althoughthe exemplary configuration shown in FIG. 8 shows other gate voltages(different from Vgk) directly generated via common nodes of a commonresistive divider (Rdl, . . . , Rdn), other biasing schemes forproviding such gate voltages, such as, for example, as described in theabove referenced U.S. Pat. No. 9,843,293, the disclosure of which isincorporated herein by reference in its entirety. may also beenvisioned.

It should be noted that although the above embodiments according to thepresent disclosure are presented with respect to a stacked cascodeamplifier which is shown to be powered by a substantially fixed supplyvoltage, V_(DD), such as, for example, a battery voltage, otherconfigurations of such stack cascode amplifier where the supply voltageis variable can also be envisioned. In some exemplary configurations,the supply voltage can be a voltage regulator, or a DC-DC converter. Infurther exemplary configurations, the supply voltage can vary undercontrol of an external control signal. In some configurations, thecontrol signal can be a function of an envelope signal of the input RFsignal, RF_(in), or the output RF signal, RF_(out). Detailed descriptionof such amplifiers operating from a variable supply voltage can befound, for example, in the above referenced U.S. Pat. Nos. 9,716,477,9,219,445, and 9,413,298, the disclosures of which are incorporatedherein by reference in their entirety. A person skilled in the art wouldalso know of configurations where the supply to the amplifier is in theform of a current source instead of the exemplary voltage source (e.g.,V_(DD)) discussed in the present disclosure. The teachings according tothe present disclosure equally apply to such diverse supplyconfigurations. The exemplary case of a (substantially) fixed supplydiscussed in the present disclosure should not be considered as limitingwhat the applicant considers to be the invention. Furthermore, althoughan exemplary non-limiting case of a single ended RF amplifierconfiguration is discussed in the above embodiments, the teachingsaccording to the present disclosure equally apply to other amplifierconfigurations using stacked transistors, such as, for example,differential configurations. Some such configurations are described in,for example, the above referenced U.S. Pat. No. 9,413,298, thedisclosure of which is incorporated herein by reference in its entirety.

Although N-type MOSFETs are used to describe the embodiments in thepresent disclosure, a person skilled in the art would recognize thatother types of transistors such as, for example, P-type MOSFETs andbipolar junction transistors (BJTs) can be used instead or incombination with the N-type MOSFETs. Furthermore, a person skilled inthe art will also appreciate the advantage of stacking more than twotransistors, such as three, four, five or more, provide on the voltagehandling performance of the amplifier. This can for example be achievedwhen using non bulk-Silicon technology, such as insulatedsilicon-on-insulator (SOI) or Silicon-on-Sapphire (SOS) technologies. Ingeneral, individual devices in the stack can be constructed using CMOS,silicon germanium (SiGe), gallium arsenide (GaAs), gallium nitride(GaN), bipolar transistors, or any other viable semiconductor technologyand architecture known. Additionally, different device sizes and typescan be used within the stack of devices.

It should be noted that the various embodiments of the biasing circuitsaccording to the present disclosure, may be implemented as amonolithically integrated circuit (IC) according to any fabricationtechnology and process known to a person skilled in the art.

Applications that may include the novel apparatus and systems of variousembodiments include electronic circuitry used in high-speed computers,communication and signal processing circuitry, modems, single ormulti-processor modules, single or multiple embedded processors, dataswitches, and application-specific modules, including multilayer,multi-chip modules. Such apparatus and systems may further be includedas sub-components within a variety of electronic systems, such astelevisions, cellular telephones, personal computers (e.g., laptopcomputers, desktop computers, handheld computers, tablet computers,etc.), workstations, radios, video players, audio players (e.g., mp3players), vehicles, medical devices (e.g., heart monitor, blood pressuremonitor, etc.) and others. Some embodiments may include a number ofmethods.

The term “amplifier” as used in the present disclosure is intended torefer to amplifiers comprising single or stacked transistors configuredas amplifiers, and can be used, for example, as power amplifiers (PAs)and/or low noise amplifiers (LNAs). An amplifier can refer to a devicethat is configured to amplify a signal input to the device to produce anoutput signal of greater magnitude than the magnitude of the inputsignal. Stacked transistor amplifiers are described for example in U.S.Pat. No. 7,248,120, issued on Jul. 24, 2007, entitled “StackedTransistor Method and Apparatus”, U.S. Pat. No. 7,123,898, issued onOct. 17, 2006, entitled “Switch Circuit and Method of Switching RadioFrequency Signals”, U.S. Pat. No. 7,890,891, issued on Feb. 15, 2011,entitled “Method and Apparatus Improving Gate Oxide Reliability byControlling Accumulated Charge”, and U.S. Pat. No. 8,742,502, issued onJun. 3, 2014, entitled “Method and Apparatus for use in ImprovingLinearity of MOSFETs Using an Accumulated Charge Sink—Harmonic WrinkleReduction”, the disclosures of which are incorporated herein byreference in their entirety. As used herein, the term “amplifier” canalso be applicable to amplifier modules and/or power amplifier moduleshaving any number of stages (e.g., pre-driver, driver, final), as knownto those skilled in the art.

The term “MOSFET”, as used in this disclosure, means any field effecttransistor (FET) with an insulated gate and comprising a metal ormetal-like, insulator, and semiconductor structure. The terms “metal” or“metal-like” include at least one electrically conductive material (suchas aluminum, copper, or other metal, or highly doped polysilicon,graphene, or other electrical conductor), “insulator” includes at leastone insulating material (such as silicon oxide or other dielectricmaterial), and “semiconductor” includes at least one semiconductormaterial.

As should be readily apparent to one of ordinary skill in the art,various embodiments of the invention can be implemented to meet a widevariety of specifications. Unless otherwise noted above, selection ofsuitable component values is a matter of design choice and variousembodiments of the invention may be implemented in any suitable ICtechnology (including but not limited to MOSFET structures), or inhybrid or discrete circuit forms. Integrated circuit embodiments may befabricated using any suitable substrates and processes, including butnot limited to standard bulk silicon, silicon-on-insulator (SOI), andsilicon-on-sapphire (SOS). Unless otherwise noted above, the inventionmay be implemented in other transistor technologies such as bipolar,GaAs HBT, GaN HEMT, GaAs pHEMT, and MESFET technologies. However, theinventive concepts described above are particularly useful with anSOI-based fabrication process (including SOS), and with fabricationprocesses having similar characteristics. Fabrication in CMOS on SOI orSOS enables low power consumption, the ability to withstand high powersignals during operation due to FET stacking, good linearity, and highfrequency operation (i.e., radio frequencies up to and exceeding 50GHz). Monolithic IC implementation is particularly useful sinceparasitic capacitances generally can be kept low (or at a minimum, keptuniform across all units, permitting them to be compensated) by carefuldesign.

Voltage levels may be adjusted or voltage and/or logic signal polaritiesreversed depending on a particular specification and/or implementingtechnology (e.g., NMOS, PMOS, or CMOS, and enhancement mode or depletionmode transistor devices). Component voltage, current, and power handlingcapabilities may be adapted as needed, for example, by adjusting devicesizes, serially “stacking” components (particularly FETs) to withstandgreater voltages, and/or using multiple components in parallel to handlegreater currents. Additional circuit components may be added to enhancethe capabilities of the disclosed circuits and/or to provide additionalfunctionality without significantly altering the functionality of thedisclosed circuits.

A number of embodiments according to the present disclosure have beendescribed. It is to be understood that various modifications may be madewithout departing from the spirit and scope of such embodiments. Forexample, some of the steps described above may be order independent, andthus can be performed in an order different from that described.Further, some of the steps described above may be optional. Variousactivities described with respect to the methods identified above can beexecuted in repetitive, serial, or parallel fashion.

It is to be understood that the foregoing description is intended toillustrate and not to limit the scope of the disclosure, which isdefined by the scope of the following claims, and that other embodimentsare within the scope of the claims. (Note that the parenthetical labelsfor claim elements are for ease of referring to such elements, and donot in themselves indicate a particular required ordering or enumerationof elements; further, such labels may be reused in dependent claims asreferences to additional elements without being regarded as starting aconflicting labeling sequence).

What is claimed:
 1. A circuit arrangement comprising: a stacked cascodeamplifier comprising an input transistor and one or more cascodetransistors, the one or more cascode transistors comprising an outputtransistor, wherein the input transistor is configured to receive an RFsignal and the output transistor is configured to output an amplifiedversion of the RF signal; a reference circuit comprising a scaled downversion of the stacked cascode amplifier, the reference circuit coupledto the stacked cascode amplifier via respective gate nodes; and abiasing circuit configured to provide a biasing voltage to at least onegate node of a transistor of the one or more cascode transistors and agate node of a respective transistor of the reference circuit, whereinthe biasing circuit comprises a feedback loop that senses a voltage at asource node of the respective transistor of the reference circuit andcontrols the biasing voltage to the at least one gate node so that asensed voltage at said source node is equal to a reference voltage,wherein control of the biasing voltage is provided by charging anddischarging of a capacitor that is coupled between said gate node and areference ground by a current output by the feedback loop; and whereincoupling of the stacked cascode amplifier to the reference circuit isprovided via respective series connected resistors that are configuredto substantially isolate the reference circuit from the RF signal. 2.The circuit arrangement according to claim 1, wherein the feedback loopcomprises an operational amplifier comprising a positive input coupledto the reference voltage, a negative input coupled to the source node ofthe respective transistor of the reference circuit, and an outputcoupled to the at least one gate node, the output configured to outputthe current for charging and discharging of the capacitor.
 3. Thecircuit arrangement according to claim 2, wherein the reference voltageis generated via a resistive voltage divider comprising two seriesconnected resistors.
 4. The circuit arrangement according to claim 3,wherein the two series connected resistors comprise at least oneconfigurable resistor.
 5. The circuit arrangement according to claim 3,wherein a current through the resistive voltage divider is 1 μA or less.6. The circuit arrangement according to claim 2, wherein a magnitude ofthe current output by the of the operational amplifier is independentfrom a magnitude of a current that generates the reference voltage. 7.The circuit arrangement according to claim 1, wherein a scale of thereference circuit with respect to the stacked cascode amplifier is 1/20or less.
 8. The circuit arrangement according to claim 1, wherein the atleast one gate node is a gate node of the output transistor.
 9. Thecircuit arrangement according to claim 1, wherein the at least one gatenode is a gate node of a transistor that is connected to the inputtransistor.
 10. The circuit arrangement according to claim 1, whereinthe at least one gate node is a gate node of a transistor that is notthe output transistor and that is not connected to the input transistor.11. The circuit arrangement according to claim 1, wherein: the one ormore cascode transistors comprises a plurality of cascode transistors,the biasing circuit is further configured to provide an additionalbiasing voltage to a gate node of an additional transistor of theplurality of cascode transistors and a gate node of a respectiveadditional transistor of the reference circuit, wherein the biasingcircuit further comprises an additional feedback loop that senses avoltage at a source node of the respective additional transistor of thereference circuit and controls the additional biasing voltage so that asensed voltage at said source node is equal to an additional referencevoltage.
 12. The circuit arrangement according to claim 11, whereincontrol of the additional biasing voltage is provided by charging anddischarging of an additional capacitor that is coupled between the gatenode of said additional transistor and the reference ground by a currentoutput by the additional feedback loop.
 13. The circuit arrangementaccording to claim 11, wherein the reference voltage and the additionalreference voltage are generated via one resistive voltage dividercomprising a plurality of series connected resistors.
 14. The circuitarrangement according to claim 13, wherein the plurality of seriesconnected resistors comprise at least one configurable resistor.
 15. Thecircuit arrangement according to claim 1, wherein the input transistoris coupled to a reference ground via a degeneration inductor.
 16. Thecircuit arrangement according to claim 15, wherein the stacked cascodeamplifier is a low noise amplifier (LNA) used in a receive path of an RFsystem.
 17. The circuit arrangement according to claim 1, wherein theinput transistor, the one or more cascode transistors, and respectivetransistors of the reference circuit are FET transistors.
 18. Thecircuit arrangement according to claim 17, wherein the FET transistorsare fabricated using one of: a) silicon-on-insulator (SOI) technology,and b) silicon-on-sapphire technology (SOS).
 19. An electronic modulecomprising the circuit arrangement of claim
 1. 20. A circuit arrangementcomprising: a stacked transistor amplifier comprising an inputtransistor and one or more stack transistors, the one or more stacktransistors comprising an output transistor, wherein the inputtransistor receives an RF signal and the output transistor outputs anamplified version of the RF signal; a reference circuit comprising ascaled down version of the stacked transistor amplifier, the referencecircuit and the stacked transistor amplifier being coupled to oneanother at corresponding gate nodes; and a biasing circuit configured toprovide a biasing voltage to at least one gate node of a transistor ofthe one or more stack transistors and a corresponding gate node of atransistor of the reference circuit, wherein the biasing circuitcomprises a feedback loop that senses a voltage at a source node of therespective transistor of the reference circuit and controls the biasingvoltage to the at least one gate node so that a sensed voltage at saidsource node is equal to a reference voltage, wherein control of thebiasing voltage is provided by charging and discharging of a capacitorthat is coupled between said gate node and a reference ground by acurrent output by the feedback loop, and wherein coupling of the stackedtransistor amplifier to the reference circuit is provided via respectiveseries connected resistors that are configured to substantially isolatethe reference circuit from the RF signal.
 21. The circuit arrangementaccording to claim 20, wherein substantial isolation of the referencecircuit from the RF signal allows for a higher gain of the feedbackloop.
 22. The circuit arrangement according to claim 20, whereincharging and discharging of the capacitor is through a series connectedresistor of the respective series connected resistors that is coupled tothe at least one gate node.